1. Field of the Invention
The invention relates to a tapered roller bearing.
2. Description of Related Art
In the related art, a tapered roller bearing is known that includes an inner ring, an outer ring, a plurality of tapered rollers, and a cage. Such tapered roller bearing is used, for example, to support a shaft built in a gear mechanism of a transmission, a differential device, and the like in an automobile serving as a power transmitting device.
The tapered roller bearing pressures tapered rollers from an axial direction when the tapered rollers are assembled between the inner ring and the outer ring so that a shaft, rotatably supported by the relevant bearing, in a radial direction and an axial direction is accurately positioned and an run-out of the shaft is suppressed. The tapered rollers are each subjected to downward roller displacement of being sufficiently sunk until a roller large end face, which is a large diameter side end face of the tapered roller, contacts with a cone back face rib (hereinafter, referred to as a large rib) end face on an axially inward side of a large rib portion of the inner ring by such pressuring. In an assembled state in which a rolling contact surface of the tapered roller is brought into contact with raceway surfaces of the inner and outer rings in a deviated manner, a compression load is repeatedly applied to the rolling contact surface and the raceway surfaces of the inner and outer rings thus arising a concern for fatigue flaking (fatigue damage) at an early stage, and hence the downward roller displacement is required to suppress such early stage flaking.
An amount by which the tapered roller moves in the axial direction such that the roller large end face contacts with the large rib end face of the inner ring by the downward roller displacement is referred to as an upward roller displacement. In terms of design, the tapered roller bearing is set such that the length of the inner ring raceway surface of the inner ring (distance between cone front face rib (hereinafter referred to as small rib and large rib)) is larger than the length of the rolling contact surface of the tapered roller, and the upward roller displacement is determined by such setting. An example of a structure in which a convex portion is formed on an outer circumferential surface of the cage is disclosed as a technique for reducing the downward roller displacement failure caused by the variation in the pressuring (see e.g., Japanese Patent Application Publication No. 11-210759 (JP 11-210759 A)).
In the technique of JP 11-210759 A, however, the assembly efficiency degrades if the downward roller displacement takes a long time and thus a concern for increase in the manufacturing cost arises. A concern for the early stage flaking easily arises if the downward roller displacement is insufficient. Furthermore, since a plurality of the tapered rollers are disposed in the axial direction, the positions of all the tapered rollers with respect to the inner ring are assumed to be not uniform before the pressuring. A concern for the downward roller displacement failure caused by the variation in the positions of the tapered rollers thus arises. Such downward roller displacement failure is more significant when the tapered roller is deviated to a side opposite to the downward roller displacement direction in the assembly direction of the tapered roller bearing.